Steady state fluid flow verification for sample takeoff

ABSTRACT

A system and method for substantially coincidental sample takeoff flow rate verification which detects unstable flow conditions in a pipeline, terminates fluid sample analysis during flow instability, and resumes sample takeoff when a steady flow state is re-established.

FIELD OF INVENTION

This invention relates to an improvement providing enhanced reliabilityof obtained measurements in the field of gas sample analysis. Theinvention provides substantially coincidental verification of steadystate fluid flow during analytical sample takeoff, particularly suitablefor use with cryogenic fluids such as liquid natural gas (LNG).

BACKGROUND OF THE INVENTION

Gas quality, quantity, and energy measurement in the context of fuels,particularly in custody transfer from a pipeline or source, requiressample takeoff and conditioning. It is known that variations in samplemeasurements may be caused, for example, by fluid flow irregularities,component partitioning, and/or phase separation either before or duringthe sample extraction process. The presence of flow pulsations,non-laminar flow, and extracted sample lag time are some of therecognized problems that undermine sufficient sample flow uniformity toprevent accurate analysis.

Standard sampling practices in the LNG industry, particularly in thecontext of custody transfer operation, typically are made when the LNGis at specified levels in a static storage container or based onobservations of the physical flow state in a pipeline when a stable flowrate is believed to have been achieved. During periods of instability orerratic flow, sample extraction and analysis is typically suspendeduntil acceptable conditions resume. Governing standards for the samplingof liquefied natural gas, such as ISO 8943:2007, Chapter 7.1 states thatsampling should only occur during “ . . . that period of time duringwhich the flow rate is sufficiently stable . . . ” The standard does notdefine any particular method to quantify the stated “stable” condition.However, in the absence of a readily apparent problem, the steady stateflow determination conventionally is made only after the fact. That is,only after passing through the analyzer and detecting variations inobtained analytical results beyond a permissible threshold does thestability of the sample flow become suspect. Consequently, the validityof the obtained results is problematic and the accuracy of the resultsfor context energy audits in custody transfer or the like often becomesunreliable. Existing systems and apparatus for flow analysis of fluidsin pipelines do not address the problem associated with sample takeoffduring unstable flow conditions and therefore overlook the resultingproblems with measurement/analytical accuracy.

What is needed is a system integrated or associated with sample takeoffequipment for substantially coincidental verification of a steady flowstate of the sampled fluid.

SUMMARY OF THE INVENTION

It is an object of the present invention in certain embodiments toprovide a system for determining when the flow of fluids through apipeline take on a substantially stable and steady flow stateappropriate for sample extraction and analysis.

It is another object of the invention to provide at least one method ofstable flow verification prior to introducing an extracted sample toanalytical equipment for conducting sample analysis.

It is another object of the invention in certain embodiments to providea system and method for improving the accuracy of analyticalmeasurements taken from samples over an extended period of time, whichmay include periods of sample flow instability.

A further object of the invention in certain embodiments is to provide atechnique for detecting sample flow stability at the time of sampleextraction for improved quality to sample analysis.

Still another object of the invention in certain embodiments is todiscontinue sample takeoff during periods of flow instability.

A further object of the invention in certain embodiments is to provide asystem and method for substantially coincidental flow rate verificationwith sample takeoff from a fluid containing source.

Certain of these and other objects are satisfied by a sample takeoffsystem for cryogenic fluids in a pipeline comprising: a sample takeoffprobe; a power-operated valve associated with said sample takeoff probefor controlling sample takeoff by the probe; and a detector of fluidflow status in the pipeline located proximately to the sample takeoffprobe, said detector generating at least one control signal communicatedto said power-operated valve to terminate sample takeoff from thepipeline during fluid flow instability.

Still certain objects and others may be satisfied by a fluid pipelinesample takeoff system for substantially coincidental flow rateverification, comprising: a sample takeoff probe; a sound wave detectorfor detecting the presence of acoustic anomalies generated by at leastone unstable flow condition of the fluid in the pipeline and generatinga signal representative thereof; a controller for receiving the signaland determining if the signal exceeds a select threshold; and anelectro-mechanically actuated valve associated with the sample takeoffprobe and in signal communication with the controller, saidelectro-mechanically actuated valve being operational to terminate fluidsample extraction upon detection of a threshold exceeding signal and toresume fluid sample extraction from the pipeline upon receipt of asignal not exceeding the select threshold and indicative ofreestablishment of a substantially steady flow state.

The foregoing and still other objects of the invention are satisfied bya method for selectively actuating fluid sample extraction by a probefrom a pipeline, comprising the steps of: detecting flow conditions of afluid in a pipeline; generating a detection signal corresponding to adetected signal generated by the flow conditions of the fluid in thepipeline; communicating the detection signal to a controller whichdetermines if the signal exceeds a pre-select threshold indicative offluid flow instability; and causing a solenoid actuated valve toterminate sample fluid extraction from the pipeline upon detection of athreshold exceeding signal and to resume sample fluid extraction upondetection of a signal less than the pre-selected threshold correspondingto substantially steady state fluid flow.

The present invention contemplates steady state flow verification at thefront end of the takeoff system, not the back end. In contrast toexisting LNG (cryogenic) or NGL (non-cryogenic) sample conditioning andanalysis systems, the present invention contemplates pre-analyzerdetection of fluid flow stability. Such detection avoids sample flowinstability and the concomitantly undesirable variations in obtainedresults from an analyzer. The present invention also avoids wastingresources and time associated with sample rejection following thedetection of variation only after completing sample analysis. In thecontext of custody transfer energy content auditing, the inventionprovides an enhanced degree of confidence in the obtained results.

In theory, the invention relies on sensor detection based on thebehavior of sound waves of sufficient frequency (acoustic/ultrasonic).At such frequencies, sound waves mechanically propagate efficiently inliquids, less efficiently in gases, and virtually not at all in mixturesof the two. In a substantially uniform liquid of a specific composition,the speed of sound is relatively high and attenuation is substantiallyless than in gas of a like composition. Consequently, as ascertained byacoustic measurement, the signal generated by a liquid or liquid/gasmixture in a pipeline can be utilized to determine if a stable flowexists within the pipeline for sample extraction. When sample extractionoccurs during steady/stable flow of the sampled stream, more accurateand reliable results are obtained and the requirements of ISO 8943:2007are achieved.

In one arrangement contemplated by the invention, an acoustical sensoris mounted (either permanently or removably) at or near a sample takeoffprobe on a pipeline, for example an LNG transfer. The sensor may bewetted (in contact with the fluid) or placed external to the process,for example, clamp-on. The sensor is in signal communication through anappropriate connection to a sound wave processor/electronic analysisdevice for measuring one or a combination of the following sixcharacteristics:

A. The speed of sound of an ultrasonic signal through the fluid (activemeasurement): In the case of LNG, the speed of sound is a function ofits temperature, pressure, and composition. It is not a function of theLNG's velocity through the pipeline (i.e. flow rate). Any detectedvariation in the speed of sound is an indication that at least one ofthese characteristics (i.e. temperature, pressure, or composition) ofthe LNG is changing during the timeframe of the measurement andindicates sample instability.

B. The attenuation of the ultrasonic signal through the fluid (activemeasurement): In the case of LNG, the ultrasonic attenuation coefficientagain is strictly a function of its temperature, pressure, and/orcomposition. A detected variation of signal strength propagating througha known LNG quantity is an indication of an unstable flow state.

C. The change in frequency components of the ultrasonic signal havingpassed through the fluid (active measurement): As is the case with soundspeed and attenuation, a frequency shift in a detected ultrasonic pulsetraveling through a known quantity of LNG is indicative of flowinstability.

D. The amplitude and frequency spectrum of the mechanical energygenerated by the flowing LNG (passive measurement): Flowing liquids inpipelines generate specific levels and frequencies of acoustic energy,or noise. Acoustic or ultrasonic sensors can measure the characteristicsof the mechanical energy by passively ‘listening’. Changes to the noisegenerated by flowing LNG within a pipeline are indicators of unstableflow.

E. The physical level of liquid flowing in the pipeline: An ultrasonicsignal may be used to determine the level of liquid in the pipeline bydetecting the liquid/gas interface, due to the measured reflectionthrough the liquid. A variation in the detection level is a directindicator that the flow rate is unstable.

F. The physical level of gas flowing in the pipeline: An ultrasonicsignal may be used to determine the gas or vaporized liquid level in thepipeline by detecting the liquid/gas interface due to the measuredreflection through the gas/vapor. A variation in the detection level isa direct indicator that the flow rate is unstable.

The invention contemplates a diagnostic tool that effectively limitssample takeoff to times when appropriate sample flow conditions exist,for example the presence of a steady flow state. The system monitorsflow in the pipeline at or closely proximate to the time of takeoff of asample, which is then directed to an associated sample conditioner. Theinvention features takeoff valving triggered to terminate sample takeoffupon detection of a flow variation beyond an allowable threshold and torestart sample takeoff upon resumption of a steady flow state. To thisend, the present invention, in one embodiment, recognizes the presenceof an appropriate detection flow state window based on attenuationcoefficients derived from signal propagation through the pipeline sourceof the sampled/extracted fluid.

Another embodiment starts with a basic assumption of using ultrasound toascertain the propagation of sound waves through the pipeline. A passiveembodiment, in theory “listens” to the noise in the pipeline with anexternal sensor mounted thereon near the extraction probe and generatesa baseline of noise under nominal flow conditions. Variations of thenoise characteristics beyond an established threshold will trigger analarm signal and/or automatic shutoff of sample extraction until thebaseline is re-established. In other words, if the noise level isoutside the threshold boundary during the transfer process, there is anindication of flow disruption caused by irregularities, e.g., bubbles,cavitation, pulsation (from pumping), vapor formation, fluid compositionchanges from component partitioning, etc. In the presence of suchconditions, direct detection of the anomaly prevents introduction of thecompromised fluid to the downstream conditioning equipment and gasanalyzer.

Particular terminology used herein is for the purpose of describingparticular embodiments only and is not intended to be limiting of theinvention.

As used herein, the singular forms, “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the root terms “include”and/or “have”, when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of at least one other feature,step, operation, element, component, and/or groups thereof.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus.

For definitional purposes and as used herein “connected” includesphysical attachment, whether direct or indirect, permanently affixed oradjustably mounted, as for example, the vaporizer is connected to thetakeoff probe. Thus, unless specified, “connected” is intended toembrace any operationally functional connection.

References to “one embodiment”, “an embodiment”, or “in embodiments”mean that the feature being referred to is included in at least oneembodiment of the invention. Moreover, separate references to “oneembodiment”, “an embodiment”, or “embodiments” do not necessarily referto the same embodiment; however, neither are such embodiments mutuallyexclusive, unless so stated, and except as will be readily apparent tothose skilled in the art. Thus, the invention can include any variety ofcombinations and/or integrations of the embodiments described herein.

As used herein, “integrated” and “integral” is intended to connote atleast two cooperative, separable, discrete components being combinableinto or mated/combined into a single integrated structure.

As used herein, and unless expressly stated to the contrary, “or” refersto an inclusive-or and not to an exclusive-or. For example, a conditionA or B is satisfied by any one of the following: A is true (or present)and B is false (or not present), A is false (or not present) and B istrue (or present), and both A and B are true (or present).

As used herein “substantially,” “generally,” and other words of degreeare relative modifiers intended to indicate permissible variation fromthe characteristic so modified. It is not intended to be limited to theabsolute value or characteristic which it modifies but rather possessingmore of the physical or functional characteristic than its opposite, andpreferably, approaching or approximating such a physical or functionalcharacteristic.

As used herein, “power-operated valve” contemplates an automaticallyoperated valve actuated by any of electrical, hydraulic, or pneumaticenergy and, more preferably, an electro-mechanically actuated valve suchas a solenoid valve.

As used herein, “unitary” is intended to connote anindivisible/undivided single structure.

In the following description, reference is made to the accompanyingdrawings, and which are shown by way of illustration to the specificembodiments in which the invention may be practiced. The followingillustrated embodiments are described in sufficient detail to enablethose skilled in the art to practice the invention. It is to beunderstood that other embodiments may be utilized and that structuralchanges based on presently known structural and/or functionalequivalents may be made without departing from the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the basic components of the invention.

FIG. 2 illustrates an embodiment of the invention where the flow sensoris positioned in the pipeline proximate to the sample takeoff probe.

FIG. 3 schematically represents alternative potential embodiments of theinvention where the flow sensor is disposed in at least one of threedifferent locations within the sampling system.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in schematic form, an embodiment of the inventiveSteady-State-Flow (SSF) detection system 10. At a most fundamentallevel, the SSF system 10 of the invention comprises a detection systemhaving a sonic sensor 12 mounted into a flowing stream of cryogenicfluid F (illustrated in FIG. 2), an electronic controller 14, whichenergizes and measures signals from the sensor 12, and an expertsoftware system 16 to configure and communicate with the controller 14.The controller 14 is connected to a shutoff solenoid valve 18 thatterminates sample takeoff when flow instability is detected.

In ordinary operation, the ultrasonic measurement system is affixed tothe pipeline P. Typically, if active, the array will include anultrasonic transmitter and an ultrasonic receiver. If passive, only asound detector is necessary. In either case, the system 10 is preferablyconnected electronically to a microchip or PLC for receiving theincoming signal 20, processing the signal according to the selectedprotocol/algorithm, detecting variations beyond a permitted threshold,generating a signal responsive to the detected variation for appropriateaction, i.e., closing a solenoid-controlled valve 18 to terminate sampletakeoff, generating an alarm, etc. Only upon resumption of a steady flowstate would sample takeoff be re-established.

The particular form of the sensor 12 would depend upon the desiredfunctionality of the unit, which is contingent on the selected techniqueor combinations thereof for active or passive measurements. Regardlessof the selected parameter or parameters utilized for steady state flowdetermination (i.e., ultrasonic wave propagation, ultrasonic waveattenuation, ultrasonic wave boundary reflection, passive noisedetection, etc.), the sensor 12 is preferably in connection with asolenoid valve 18, associated with the probe 22 and intermediatelydisposed in-line between the probe 22 and the down-stream sampleanalyzer, to be opened during a substantially steady flow state.

The sensor 12 may be in the form of a stand-alone detector (passive) ora wave source generator/transmitter and receiver (active) either in aunitary housing (reflection) or diametrically separated. The sensor 12may be set in a permanently affixed mounting on a pipeline P,selectively positionable using a clamping array or even temporarilymounted using a flexible belt for easy placement and removal.Preferably, the sensor 12, whether in unitary form or having separatetransmitter/receiver elements, is located proximate to an associatedsample takeoff probe 22 on the pipeline P to facilitate substantiallyco-incident flow verification of pipeline fluids F, as illustrated bythe embodiment in FIG. 2.

In the context of operation, using a combination of the foregoingapproaches and even relying on different sensing functionalities, forexample, direct (speed of sound/attenuation coefficient and frequencychange/delta) or indirect (noise detection from cavitation/bubbles), canminimize potential inaccuracies arising from flow irregularities of acryogenic fluid F, like LNG, when the conditions (temperature/pressure)are near the fluid's phase boundary.

FIG. 3 illustrates alternative potential embodiments of the inventionwhere the sensor 12 is at different locations within the samplingsystem. These include within the pipeline P, which comprises thearrangement depicted in FIG. 2. Alternatively, the sensor 12 may bepositioned “downstream” of the takeoff, as for example in the takeoffsample tubing 24 for communicating the sample from the pipeline P to thesample conditioning cabinet, which preferably provides a thermalinsulating capability by employing vacuum jacketed tubing or the like. Asensor 12 can also be placed in a passive housing that the sample ispassed through following takeoff, such as an unheated PONY® box.

The further option for sensor placement in accordance with the inventionis to dispose the sensor 12 at the entry port into the vaporizer cabinet26 to sense the sample flow state prior to sample conditioning.

In the context of the sample take-off control, so long as thepower-operated valve is substantially immediately actuable to open andclose dependent upon pipeline flow conditions, while preferably aconventional electromechanical solenoid valve, the valve may be based onother known sources of motive force such as hydraulic, fluidic, orpneumatic systems that can actuate valve shutoff upon detection of flowinstability by a connected sensor.

Although selected embodiments of the invention have been described inthe forgoing specification, it is understood by those skilled in the artthat many modifications and embodiments of the invention will come tomind to which the invention pertains, having benefit of the teachingpresented in the foregoing description and associated drawing. It istherefore understood that the invention is not limited to the specificembodiments disclosed herein, and that many modifications and otherembodiments of the invention are intended to be included within thescope of the invention. Moreover, although specific terms are employedherein, they are used only in a generic and descriptive sense, and notfor purposes of limiting the description of the invention.

We claim:
 1. A sample takeoff system for fluids in a pipelinecomprising: a sample takeoff probe; a power-operated valve associatedwith said sample takeoff probe for controlling sample takeoff by theprobe; and a sensor of fluid flow status in the pipeline locatedproximately to the sample takeoff probe for detecting the stability offluid flow in the pipeline, said sensor configured to generate at leastone control signal communicated to said power-operated valve toterminate sample takeoff from the pipeline during fluid flowinstability, where the sensor is configured to sense sound waves in thefrequency range selected from the group consisting of ultrasonic,audible, and infrasonic to monitor pipeline fluid flow status.
 2. Thesample takeoff system of claim 1 further comprising: an electroniccontroller for receiving the communicated signal from the sensor,wherein the power-operated valve being an electrically actuated solenoidvalve.
 3. The sample takeoff system of claim 2 further comprising:software for signal processing and control of the solenoid valve.
 4. Thesample takeoff system of claim 1 where the sensor is a sonic sensor. 5.The sample takeoff system of claim 1 where the sensor is configured tosense fluid flow instability in the pipeline beyond a permissiblethreshold from anomalies generated by any of pulsations, phasetransitions, and non-laminar flow.
 6. The sample takeoff system of claim5 where the sensor is passive, mounted externally on the pipeline,provides a baseline signal corresponding to noise generation at nominalflow conditions associated with flow uniformity and communicates asignal upon detecting noise at a select threshold exceeding the baselinesignal where said baseline signal is representative of an acousticalsignal in the range selected from the group consisting of ultrasonic,audible, and infrasonic.
 7. The sample takeoff system of claim 6 wherethe sensor is associated with an ultrasonic wave source generator. 8.The sample takeoff system of claim 7 where the sensor is configured tomeasure fluid flow by one of ultrasonic wave propagation, ultrasonicwave attenuation or ultrasonic wave boundary reflection.
 9. The sampletakeoff system of claim 8 where the ultrasonic wave source generator isdiametrically separated from the sensor on the pipeline.
 10. A fluidpipeline sample takeoff system for substantially coincidental flow rateverification, comprising: a sample takeoff probe; a sensor for detectingthe presence of anomalies generated by at least one unstable flowcondition of the fluid in the pipeline and generating a signalrepresentative thereof; a controller configured to receive the signaland determine if the signal exceeds a select threshold; and anelectro-mechanically actuated valve associated with the sample takeoffprobe and in signal communication with the controller, saidelectro-mechanically actuated valve configured to terminate fluid sampleextraction upon detection of a threshold exceeding signal and to resumefluid sample extraction from the pipeline upon receipt of a signal notexceeding the select threshold and indicative of reestablishment of asubstantially steady flow state, where the sensor is configured to sensesound waves in the frequency range selected from the group consisting ofultrasonic, audible, and infrasonic to monitor pipeline fluid flowstatus.
 11. The fluid pipeline sample takeoff system of claim 10 furthercomprising: an ultrasonic transmitter for transmitting an ultrasonicsignal into the fluid for analysis of fluid flow selected from the groupconsisting of ultrasonic wave propagation, ultrasonic wave attenuationand ultrasonic wave boundary attenuation.
 12. The fluid pipeline sampletakeoff system of claim 10 further comprising: an ultrasonic transmitterfixed on the exterior of the pipeline diametrically opposed to thesensor.
 13. A method for selectively actuating fluid sample extractionby a probe from a pipeline, comprising the steps of: detecting flowconditions of a fluid in a pipeline via a sensor that senses sound wavesin the frequency range selected from the group consisting of ultrasonic,audible, and infrasonic to monitor pipeline fluid flow status;generating a detection signal corresponding to a detected signalgenerated by flow conditions of the fluid in the pipeline; communicatingthe detection signal to a controller which determines if the signalexceeds a pre-select threshold indicative of fluid flow instability; andcausing a power operated valve to terminate sample fluid extraction fromthe pipeline based on the detection signal and pre-select threshold andto resume sample fluid extraction based on the pre-selected thresholdand detection signal corresponding to substantially steady state fluidflow.
 14. The method of claim 13 where the power operated valve is asolenoid valve which is actuated to close and terminate sample takeoffupon detection of a threshold exceeding signal.
 15. The method of claim13 further comprising the step of conveying the sample fluid extractedfrom the pipeline to an associated analyzer when the signal does notexceed the pre-select threshold indicative of fluid flow instability.